1. Field of the Invention
This invention relates to electrical wire and cable. More specifically, it relates to a method for manufacture of electrical wire and cable having a reduced coefficient of friction and reduced pulling force to aid in the installation of same.
2. Description of Related Art
Electrical cables used in housing and industrial projects typically include an electrical conductor surrounded by at least one additional layer. In some cases, the additional layer is an insulating layer of material used to insulate the conductor. The insulator may be made of insulating materials such as polyvinyl chloride (PVC) or polyethylene (PE). The insulating layer is then surrounded by a layer of thermoplastic material, and this outermost layer may be referred to as a “sheath” or a “jacket.” Installation of electrical cable requires the cable to be threaded or passed through sections of a building, such as walls, ceilings, ducts and other conduits. During installation of wires or cables, increased effort is required to pull the wires or cables through the conduit due to friction between the materials involved. This friction also may result in damage of the wire or cable during the installation process.
The most common electrical cable used in housing and industrial projects in the United States is called THHN (“Thermoplastic High Heat-resistant Nylon coated”). A typical THHN cable uses copper as an electrical conductor, polyvinyl chloride as the insulating material and nylon as the sheath material.
Currently, various methods are used to minimize the coefficient of friction on the surface of the wire or cable to reduce the amount of pulling force required making it easier to pull through conduit and other building structures during installation. Such methods have included manually applying a lubricant to the sheath at the job site just prior to installation. However, the manual application method is time consuming, labor intensive, and requires additional materials to be on the job site during cable installation. Other methods include adding a separate lubricating layer to the sheath and incorporating the lubricant into the sheath prior to forming the sheath. These methods typically require an additional sheath layer formed over the conductor core and insulating layer by an extrusion method or additional equipment to incorporate the lubricant into the sheath prior to formation.
Therefore, a need exists for a method of extruding a composition as an outer jacket onto wire and cable that reduces the coefficient of friction and effective pulling force required during installation that does not require spray on compositions or hand lubricating techniques.